Switch device having an insulating screen inserted between the contacts during breaking

Abstract

An electric switch in which a screen is inserted very quickly between two contacts at the moment when they part. The energy of the arc generated between the contacts inside a volume surrounded by an insulating mobile sheath is used to heat gases released, and the resulting gas pressure displaces the sheath quickly, so that the arc passing through an opening in the sheath is sheared between the sheath and the housing. This type of switch is used to advantage in protection apparatus designed to respond to an abnormal increase of the current flowing in a circuit in which they are series mounted, and in switches where rated current is high.

We claim: 
     
       1. An electric switch comprising: a casing provided with an insulating partition which delimits inside said casing first and second arc chambers and which comprises an aperture;   first and second contacts respectively housed in said arc chambers, said contacts being mobile with respect to each other between a closed position and an open position, said second contact passing through said aperture in said closed position, and   a thin mobile insulating screen mobile in a determined direction and adapted to be inserted rapidly between the contacts when said contacts are passing from said closed position to said open position so as to cause the arc arising between said contacts to be sheared between said insulating partition and said screen and the two arc chambers to be insulated from each other. wherein said mobile screen is mechanically coupled to an insulating piece which encloses, together with the casing, a variable volume such that the gas pressure raised by the arc energy when the contacts are passing from said closed position to said open position, exerts a force on the insulating piece that moves the screen in front of the aperture, causing the arc to be sheared.     
     
     
       2. An electric switch according to claim 1, wherein the mobile screen is bonded to said insulating piece and comprises a side provided with a first opening through which the mobile contact passes in the closed position, said mobile screen enclosing, with sides of the casing, a variable volume in which the first contact is housed, so that the pressure of the gases heated by the arc at the moment when the contacts pass from said closed position to said open position and exerts a force on the screen that causes it to move in front of the aperture and therefor said arc to be sheared. 
     
     
       3. An electric switch according to claim 2, wherein said screen and said insulating piece form a sheath which contains said variable volume, said sheath having a bottom which is prolonged by a continuous skirt which is parallel to said determined direction and which slides on guiding surfaces which are part of the casing. 
     
     
       4. An electric switch according to claim 3, wherein the guiding surfaces which are part of the casing are placed on an insulating portion that protrudes inside the sheath and at one and carries the first contact. 
     
     
       5. An electric switch according to claim 3, wherein the guiding surfaces which are part of the casing are placed in a seating in which the sheath slides, whilst the first contact is fastened to one end of an insulating portion of the casing that protrudes inside the sheath. 
     
     
       6. An electric switch according to claim 2, wherein the variable volume is contained inside a sheath the bottom of which is prolonged by a discontinuous skirt which is parallel to said determined direction and which slides on the surfaces of a seating which is part of the casing. 
     
     
       7. An electric switch according to claim 6, wherein the first contact is fastened to one end of an insulating portion which is part of the casing and which protrudes inside the sheath. 
     
     
       8. An electric switch according to claim 3, wherein the continuous skirt features a second opening that comes in front of a vent provided in the casing so that the gases contained within the volume can be exhausted to the atmosphere in a particular position of the sheath. 
     
     
       9. An electric switch according to claim 6, wherein the discontinuous skirt features a longitudinal indentation that comes in front of a vent provided in the casing in a particular position of the sheath. 
     
     
       10. An electric switch according to claim 5, wherein a conductor connected to the first contact runs parallel to said determined direction inside the insulating portion, whereas the second contact is carried by a support which forms a current loop with this conductor. 
     
     
       11. An electric switch according to claim 10, wherein pressure limiting devices are positioned on the sheath and on the casing respectively in such a way that the pressure in the variable volume and in the seating respectively does not exceed a present value. 
     
     
       12. An electric switch according to claim 11, wherein the second contact is assembled on a pivoting lever which is restrained in the closing position by a return spring and upon which antagonistic forces developed by an overcurrent-sensing device are brought to bear if an overload appears in its circuit. 
     
     
       13. An electric switch according to claim 12, wherein said sensing device includes a coil in which the switch current flows, and a magnetic core or frame. 
     
     
       14. An electric switch according to claim 12, wherein the said sensing device includes a U-shaped magnetizable part, the arms of which surround the contact lever. 
     
     
       15. An electric switch according to claim 13, wherein a mechanical energy accumulation device is released by a coil and core sensitive device and applies forces on the lever which are antogonistic to those developed by a contact pressure spring. 
     
     
       16. An electric switch according to claim 13, wherein the sensing device includes a coil and a magnetic core which is coupled to the sheath in order to drive the latter through a first part of its stroke during which the second contact is separated from the first contact by a sheath surface, while the sheath continues its stroke without being coupled to the magnetic core. 
     
     
       17. An electric switch according to claim 13, wherein the magnetic core of the coil is coupled to a fixed contact which can withdraw parallel to the determined direction, so as to interrupt the contact with the second contact, the latter being subjected to the action of a U-shaped magnetic structure that surrounds its support. 
     
     
       18. Switching device, wherein two switches according to claim 2 are series-mounted in the same circuit. 
     
     
       19. Switching device according to claim 18, wherein both switches have one same fixed contact located in the same sheath and two distinct mobile contacts. 
     
     
       20. Switching device according to claim 18, wherein both switches are laid out in parallel and have two mobile contacts that are electrically and mechanically coupled by a contact bridge. 
     
     
       21. Switching device according to claim 20, wherein these two switches are placed coaxially so that both sheaths move in opposite directions when opening. 
     
     
       22. An electric switch according to claim 1, wherein said first contact is a fixed contact and said second contact is a mobile contact. 
     
     
       23. An electric switch according to claim 13, wherein the magnetic core of the coil is coupled to a fixed contact which can withdraw parallel to the determined direction, so as to interrupt the contact with the second contact, the latter being subjected to the action of an energy accumulation device which is released by the movement of said core.